Communication systems are known comprising a plurality of base stations that provide communication services to remote or mobile units located in corresponding service coverage areas of the base stations. Remote unit receivers include circuits for measuring the signal strength of received signals and transmitting a received signal strength indication (RSSI) to a monitoring base station to indicate the signal strength of the carrier received by the receiver. To account for changes in RSSI as the remote unit moves and so forth, the serving base station will issue commands directing the remote unit to increase or decrease its power as the need arises. Typically, as the remote unit moves to the periphery of or into an obstructed location in the serving base station coverage area, the transmit power of the remote unit as well as the transmit power of the base station must be increased to account for an increase in path losses between the serving base station and the remote unit.
If insufficient RF power is produced by the base station transmitter to transmit a modulated carrier, the remote receiver cannot accurately demodulate voice signals and decode the data. On the other hand, if the base station's transmitter transmits the carrier signal with too much power, the performance of adjacent channels may be affected and possible jamming thereof may result.
RF power devices and circuits, such as those used in cellular telephone base stations, typically include power amplifiers. As well known, base stations are often exposed to a broad temperature range and varying RF power. In addition to variations in temperature and RF output power, there are also variations in bias voltage, frequency and load impedance. A need often arises to compensate for inadvertent changes of bias current in RF power amplifiers over temperature, power fluctuations, bias voltage frequency, or load impedance. In non-constant envelope applications such as code division multiple access (CDMA) or time division multiple access (TDMA), in particular, control of quiescent current is often needed to improve the response linearity or gain flatness of the power amplifiers, while for constant envelope applications such as the global system for mobile communications (GSM) bias voltage drop compensation is often needed to control output power or efficiency.
FIG. 1 represents a conventional system 100 for monitoring RF power device performance and handling fault management in which input and output direct current (DC) detection circuitries 101, 102, and reverse and forward RF detection circuitries 103, 104, are used to sense the operation state of the RF power device 108. They are implemented in a different chip, wafer or discrete components mounted on printed wiring board or substrate from the RF power device chip 106. The detected information is formatted by data formatting circuitry 111 and then transmitted via hardwire means 112 to separate diagnostic and control circuitry 114 used to process, interpret, and diagnose the detected information. The hardwire means 112 is typically an electrical connection made conventionally via printed traces on a printed wiring board. Fault management and control signals are relayed back to the RF power device 108 via the same hardwire means 112 on the PC board.
However, the use and reliance on the hardwire means as the communication link for the detected information and the fault management signals has problems. For instance, the hardwire electrical connection is subject to coupling from the high power RF signal associated with the operation of the nearby RF power device. This can lead to malfunctions in the circuitries, unless appropriate bypassing components are provided in the interconnect lines and circuitry, that typically increases design complexity and manufacturing costs. The hardwire means also can cause instability due to the creation of sneak feedback paths or RF loading of the RF amplifier input and output matching circuits.
Another drawback associated with conventional RF power device fault detection systems is the necessity of using an assembly of different dies, chip set or discrete components mounted on printed wiring board or substrate, to support the detection circuitries and the RF power device. Interconnecting these various separate dies for intercommunication and operation creates design, fabrication and performance issues. The off-chip arrangement of the detection circuitry can induce mismatch errors in the RF power circuitry. Also, the hardwired multi-chip arrangements are susceptible to interconnect failures, which reduces reliability. The inter-chip hardwiring arrangement also can slow the system's performance speed.
There are also conventional circuit tester systems applied to test a circuit by making use of one or more coaxial cables or optical fibers as an optical interface that physically extend between a device-under-test and a probe card, which is in turn connected to a load card and a circuit tester. As will be appreciated, communication links requiring physical interfaces between a device-under-test and a circuit tester can be more tolerable when the device-under-test is not yet installed in an enclosure or other location difficult to access under which it will be actually put into service.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are typically not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.